Hi,
at the moment I'm reviving a S5 Turbo FC which got a new engine. I took it for a first bigger test drive this week and got a problem, that I can't figure out.

When the boost picks up, the engine gets "hickups", meaning there is no straight accelration, but sudden power drops for half a second each. This only happens if the boost is above zero on the internal gauge. You can speed the car up to 100mph while keeping the boost at zero, but if it raises higher, the hickuops start. This is not affected by different rpms.
The strange part is this: If the car stands for some time (10-15min is enough) everything works for some minutes.


Any idea, where this problem comes from?

 

sounds like boost creep/overboost. pick up a boost gauge to see how much pressure the engine is pushing.

 

I'm using a Fuel Cut Defender, but it's still possible. But why should it work with the cooler engine?

 

What other modifications do you have? And what do you mean by "cooler engine"?

Perhaps you need to port both wastegate passages. -> FC3S Pro: S5 ('89-'91) Wastegate Porting

 

The engine is basicly stock. The AWS has been removed and the stock radiator was replaced with a bigger koyo. The exhaust is missing the precat, cause it was clogged. Instead there is a downpipe connected to the maincat.
The FCD was added, cause others advised me to install one after removing the precat.


With cooler engine I mean, that everything works fine after turning off the engine for a short time (10-15min is enough). My guess was, that it works while beeing slightly cooler than operating temperature and failing again when the temperature rises. But this can be a false guess.

 

i figured that because the engine is in fact hotter, not cooler. takes at least 30 minutes to actually begin cooling the bay/engine without any airflow. more heat means less boost.